San Diego Padres pitcher Mark Prior will undergo season-ending surgery on his injured right shoulder, the latest medical setback to a once-promising career.

Padres manager Bud Black announced the decision to operate before Sunday's game against the San Francisco Giants. Prior, one of the top young pitchers in the game for the Chicago Cubs just a few years ago, has not pitched in the majors since Aug. 10, 2006.

He had been trying to make a comeback with his hometown Padres this season, but his rehab process was shut down at extended spring training about two weeks ago when he had more soreness in the shoulder. Prior, 27, had surgery on the same shoulder in April 2007 while with the Cubs.

"I can't imagine how frustrated he is," Black said. "It looked like everything was on course. Then to have this happen I'm sure is extremely frustrating. I'm upset for him just because there was such confidence from him about how he felt."

The operation to repair the anterior capsule in Prior's shoulder will be performed at Scripps Clinic as early as this week by team orthopedics Dr. Heinz Hoenecke and Dr. Jan Fronek.

The Padres won't know when, or if, Prior will be able to pitch again until after the operation.